DetailedDescription

General methods to access the Key database.
To use them:
#include <kdb.h>
The kdb*() class of methods are used to access the storage, to get and
set Keys or KeySets .
The most important functions are:
o kdbOpen()
o kdbClose()
o kdbGet()
o kdbSet()
The two essential functions for dynamic information about backends are:
o kdbGetMountpoint()
o kdbGetCapability()
They use some backend implementation to know the details about how to
access the storage. Currently we have this backends:
o berkeleydb: the keys are stored in a Berkeley DB database, providing
very small footprint, speed, and other advantages.
o filesys: the key hierarchy and data are saved as plain text files in
the filesystem.
o ini: the key hierarchy are saved into configuration files.
Seealso:http://www.libelektra.org/Ini
o fstab: a reference backend used to interpret the /etc/fstab file as a
set of keys under system/filesystems .
o gconf: makes Elektra use the GConf daemon to access keys. Only the
user/ tree is available since GConf is not system wide.
Backends are physically a library named /lib/libelektra-{NAME}.so.
See writinganewbackend for information about how to write a
backend.
Language binding writers should follow the same rules:
o You must relay completely on the backend-dependent methods.
o You may use or reimplement the second set of methods.
o You should completely reimplement in your language the higher lever
methods.
o Many methods are just for comfort in C. These methods are marked and
need not to be implemented if the binding language has e.g. string
operators which can do the operation easily.

FunctionDocumentation

intkdbClose(KDB*handle)ClosesthesessionwiththeKeydatabase.
You should call this method when you finished your affairs with the key
database. You can manipulate Key and KeySet objects also after
kdbClose(). You must not use any kdb* call afterwards. You can
implement kdbClose() in the atexit() handler.
This is the counterpart of kdbOpen().
The handle parameter will be finalized and all resources associated to
it will be freed. After a kdbClose(), this handle can't be used
anymore, unless it gets initialized again with another call to
kdbOpen().
Seealso:kdbOpen()Parameters:handle contains internal information of opened key database
Returns:
0 on success
-1 on NULL pointer
ssize_tkdbGet(KDB*handle,KeySet*returned,Key*parentKey,option_toptions)Retrievekeysinanatomicanduniversalway,allotherkdbGetFunctionsrelyonthatone.
The returned KeySet must be initialized or may already contain some
keys. The new retrieved keys will be appended using ksAppendKey().
In default behaviour (options = 0) it will fully retrieve all keys
under the parentKey folder, with all subfolders and their children but
not inactive keys or folders.
The keyset will not be sorted at first place, but will be marked dirty
and sorted afterwards when needed. That could be a subsequent
ksLookup(), ksLookupByName() or kdbSet(). See ksSort() on that issue.
The behaviour can be fine-tuned with options in various ways to make
kdbGet() more comfortable.

Options

The option is an array of the following ORed flags:
o option_t::KDB_O_DEL
Its often useful to keyDel() the parentKey in the line after
kdbGet(). Using this flag, you can just pass a key allocated with
keyNew(), kdbGet() will free it for you in the end.
o option_t::KDB_O_POP
The parentKey itself will always be added to returned. If you only
want the children of the parentKey in returned, but not the parentKey
itself, use this flag. This is only valid for the first parentKey,
the one you passed. The other recursive parentKeys will stay in the
keyset. To get only the leaves of the tree, without any parentKey,
see option_t::KDB_O_NODIR below.
o option_t::KDB_O_NODIR
Don't include folders in the returned KeySet, so only keys without
subkeys. You can picture it best that you only get the leaves of the
tree of keys.
o option_t::KDB_O_DIRONLY
Put in returned only the folder keys. The resulting KeySet will be
only the skeleton of the tree. This option must not be ORed together
with KDB_O_DIR.
o option_t::KDB_O_NOSTAT
Don't stat they keys, whatever keyNeedStat() says. That means that
also the key value and comment will be retrieved. The flag will
result in that all keys in returned don't have keyNeedStat() set.
o option_t::KDB_O_STATONLY
Only stat the keys. It means that key value and comment will not be
retrieved. The resulting keys will contain only meta info such as
user and group IDs, owner, mode permissions and modification times.
You don't need that flag if the keys already have keyNeedStat() set.
The flag will result in that all keys in returned have keyNeedStat()
set.
o option_t::KDB_O_INACTIVE
Will make it not ignore inactive keys, so returned will contain also
inactive keys. Inactive keys are those that have names beginning with
'.' (dot). Please be sure that you know what you are doing, inactive
keys must not have any semantics to the application. This flag should
only be set in key browsers after explicit user request. You might
also get inactive keys when you plan to remove a whole hierarchy.
o option_t::KDB_O_SORT
Force returned to be ksSort()ed. Normally you don't want that the
returned is sorted immediately because you might add other keys or go
for another kdbGet(). Sorting will take place automatically when
needed by ksLookup() or kdbSet(), also without this option set. But
you need to sort the keyset for yourself, when you just iterate over
it. If you want to do that, pass this flag at the last kdbGet().
o option_t::KDB_O_NORECURSIVE
Don't get the keys recursive. Only receive keys from one folder.
This might not work if the backend does not support it. Be prepared
for more keys and use ksLookup() and avoid static assumptions on how
many keys you get.
Example:
KDB *handle;
KeySet *myConfig;
Key *key;
myConfig=ksNew(0);
handle = kdbOpen();
key=keyNew('system/sw/MyApp',KEY_END);
rc=kdbGet(handle,key, myConfig, 0);
keyDel(key);
key=keyNew('user/sw/MyApp',KEY_END);
rc=kdbGet(handle,key, myConfig, 0);
keyDel(key);
// will sort keyset here
key=ksLookupByName(myConfig,'/sw/MyApp/key', 0);
// check if key is not 0 and work with it...
ksDel (myConfig); // delete the in-memory configuration
// maybe you want kdbSet() myConfig here
kdbClose(handle); // no more affairs with the key database.

Details

When no backend could be found (e.g. no backend mounted) the default
backend will be used.
If you pass a NULL pointer as handle and/or returned kdbGet() will
return -1 and do nothing but keyDel() the parentKey when requested and
not a NULL pointer.
If you pass NULL as parentKey the root keys of all namespaces will be
appended to returned.
For every directory key (keyIsDir()) the appropriate backend will be
chosen and keys in it will be requested.
If any backend reports an failure the recursive getting of keys will be
stopped. Backends only report failure when they are not able to get
keys for any problems.
Parameters:handle contains internal information of opened key database
parentKey parent key or NULL to get the root keys
returned the (pre-initialized) KeySet returned with all keys found
options ORed options to control approaches
Seealso:
#option_t
kdbhigherlevelMethods that rely on kdbGet()ksLookupByName(), ksLookupByString() for powerful lookups after the
KeySet was retrieved
commandList() code in KDB::LowLevelMethods command for usage
example
commandEdit() code in KDB::LowLevelMethods command for usage
example
commandExport() code in KDB::LowLevelMethods command for usage
example
Returns:
number of keys contained by returned
-1 on failure
Key*kdbGetMountpoint(KDB*handle,constKey*where)Lookupamountpointinahandleforaspecifickey.
Will return a key representing the mountpoint or null if there is no
appropriate mountpoint e.g. its the root mountpoint.
Together with kdbGetCapability() the two essential information about
mounted backends.
Example:
Key * key = keyNew ('system/template');
KDB * handle = kdbOpen();
Key *mountpoint=0;
mountpoint=kdbGetMountpoint(handle, key);
printf('The library I am using is %s mounted in %s0,
keyValue(mountpoint),
keyName(mountpoint));
kdbClose (handle);
keyDel (key);
Parameters:handle is the data structure, where the mounted directories are
saved.
where the key, that should be looked up.
Returns:
the mountpoint associated with the key
intkdbMount(KDB*handle,constKey*mountpoint,constKeySet*config)Dynamicallymountasinglebackend.
Maps the mountpoint, defined through its name and value, into the
global elektra hierarchy. If successfull, under the mountpoint another
backend will reside.
This only works for a single KDB, that means a single thread in a
single process. You may want statically mounting by editing
system/elektra/mountpoints.
If you allocated mountpoint and config first, make sure that you free
it! It is ok to free it immediately afterwards.
Parameters:handle handle to the kdb data structure
mountpoint the keyName() of this key is the mountpoint, keyValue()
the backend
config the configuration passed for that backend
Returns:
0 on success, -1 if an error occurred
KDB*kdbOpen(void)OpensthesessionwiththeKeydatabase.
The first step is to open the default backend. With it
system/elektra/mountpoints will be loaded and all needed libraries and
mountpoints will be determined. These libraries for backends will be
loaded and with it the KDB datastructure will be initialized.
You must always call this method before retrieving or committing any
keys to the database. In the end of the program, after using the key
database, you must not forget to kdbClose(). You can use the atexit ()
handler for it.
The pointer to the KDB structure returned will be initialized like
described above, and it must be passed along on any kdb*() method your
application calls.
Get a KDB handle for every thread using elektra. Don't share the handle
across threads, and also not the pointer accessing it:
thread1 {
KDB * h;
h = kdbOpen();
// fetch keys and work with them
kdbClose(h);
}
thread2 {
KDB * h;
h = kdbOpen();
// fetch keys and work with them
kdbClose(h);
}
You don't need to use the kdbOpen() if you only want to manipulate
plain in-memory Key or KeySet objects without any affairs with the
backend key database,
Seealso:kdbClose() to end all affairs to the Key::BasicMethods database.
Returns:
a KDB pointer on success
NULL on failure
ssize_tkdbSet(KDB*handle,KeySet*ks,Key*parentKey,option_toptions)Setkeysinanatomicanduniversalway,allotherkdbSetFunctionsrelyonthatone.
The given handle and keyset are the objects to work with.
With parentKey you can only store a part of the given keyset. Otherwise
pass a null pointer or a parentKey without a name.
KeySet *ks = ksNew(0);
kdbGet (h, ks, keyNew('system/myapp',0), KDB_O_DEL);
kdbGet (h, ks, keyNew('user/myapp',0), KDB_O_DEL);
//now only set everything below user, because you can't write to system
kdbSet (h, ks, keyNew('user/myapp',0), KDB_O_DEL);
ksDel (ks);
Each key is checked with keyNeedSync() before being actually committed.
So only changed keys are updated. If no key of a backend needs to be
synced the kdbSet_backend() will be omitted.
If some error occurs, kdbSet() will stop. In this situation the KeySet
internal cursor will be set on the key that generated the error. This
specific key and all behind it were not set. To be failsafe jump over
it and try to set the rest, but report the error to the user.
Exampleofhowthismethodcanbeused:
int i;
KeySet *ks; // the KeySet I want to set
// fill ks with some keys
for (i=0; i< 10; i++) // limit to 10 tries
{
ret=kdbSet(handle,ks, 0, 0);
if (ret == -1)
{
// We got an error. Warn user.
Key *problem;
problem=ksCurrent(ks);
if (problem)
{
char keyname[300]='';
keyGetFullName(problem,keyname,sizeof(keyname));
fprintf(stderr,'kdb import: while importing %s', keyname);
} else break;
// And try to set keys again starting from the next key,
// unless we reached the end of KeySet
if (ksNext(ks) == 0) break;
}
}

Options

There are some options changing the behaviour of kdbSet():
o option_t::KDB_O_DEL
Its often useful to keyDel() the parentKey in the line after
kdbGet(). Using this flag, you can just pass a key allocated with
keyNew(), kdbGet() will free it for you in the end.
o option_t::KDB_O_SYNC
Will force to save all keys, independent of their sync state.
o option_t::KDB_O_NOREMOVE
Don't remove any key from disk, even if keyRemove() was set. With
that flag removing keys can't happen unintentional. The flag will
result in that all keys in returned don't have keyNeedRemove() set.
o option_t::KDB_O_REMOVEONLY
Remove all keys instead of setting them. All keys in returned will
have keyNeedRemove() set, but not keyNeedStat() saying to you that
the key was deleted permanently. This option implicit also activates
option_t::KDB_O_SYNC because the sync state will be changed when they
are marked remove. You might need option_t::KDB_O_INACTIVE set for
the previous call of kdbGet() if there are any. Otherwise the
recursive remove will fail, because removing directories is only
possible when all subkeys are removed.

Details

When you don't have a parentKey or its name empty, then all keys will
be set.
You can remove some keys instead of setting them by marking them with
keyRemove(). The keyNeedSync() flag will be unset after successful
removing. But the keyNeedRemove() flag will stay, but its safe to
delete the key.
Parameters:handle contains internal information of opened key database
ks a KeySet which should contain changed keys, otherwise nothing is
done
parentKey holds the information below which key keys should be set
options see in kdbSet() documentation
Returns:
0 on success
-1 on failure
Seealso:keyNeedSync(), ksNext(), ksCurrent()keyRemove(), keyNeedRemove()
commandEdit(), commandImport() code in KDB::LowLevelMethods
command for usage and error handling example
intkdbUnmount(KDB*handle,constKey*mountpoint)Dynamicallyunmountasinglebackend.
Unmount a backend that was mounted with kdbMount() before.
Parameters:handle handle to the kdb data structure
mountpoint directory where backend is mounted to, that should be
unmounted
Returns:
0 on success, -1 if an error ocurred.

Author

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